Suddenly getting "Error with start undefined"

Apologies if this has been asked before. Searched but cant find specific solution that works.

As of a few days ago I cant create new apps with my Ionic environment.

When running a basic start command:
ionic start samples sidemenu --v2

It downloads as normal, then starts the installation before failing with errors:

Installing npm packages (may take a minute or two)…
Error with start undefined
Error Initializing app: There was an error with the spawned command: npminstall
There was an error with the spawned command: npminstall

My environment is:
$ ionic info

Your system information:

Cordova CLI: 6.5.0
Ionic CLI Version: 2.2.1
Ionic App Lib Version: 2.2.0
ios-deploy version: Not installed
ios-sim version: Not installed
OS: Windows 10
Node Version: v6.10.0
Xcode version: Not installed

I have tried uninstalling / installing / upgrading Node, as suggested elsewhere.

Then, with the latest Node LTS, I try:
npm uninstall ionic -g
npm uninstall cordova -g
npm cache clean
npm install cordova -g
npm install ionic -g

and nothing seems to make any difference - always end up with the above error.

Dont know if its relevant, but I installed Git on this machine a few days ago as well… coincidence?

Hoping someone has an idea how to solve this, its a showstopper - cant create new apps!

many thanks